2ND CHAPTER: ATOMS, ELEMENTS AND
COMPOUNDS
By Aahana Singhal
TABLE OF CONTENTS
01
02
03
04
2.1
2.3
2.2
2.4
What is an atom?
● a particle of matter that uniquely
defines a chemical element.
● consists of a central nucleus that
is surrounded by one or more
negatively charged electrons.
● The nucleus is positively charged
and contains one or more relatively
heavy particles known as protons
and neutrons.
THE STRUCTURE OF THE ATOM: CARBON ATOM
ELECTRON
a negatively charged subatomic particle that
can be either bound to an atom or free (not
bound) and carries a charge equal in size to
the positive charge of an electron
PROTON
an atomic particle that occurs in the nucleus
of every atom and carries a positive charge
equal in size to the negative charge of an
electron
NEUTRON
a type of subatomic particle with no
charge (they are neutral).
6 protons
+
6
neutrons
What is an element?
● Is a substance that cannot be broken
down into anything simpler using
chemical reactions.
● This is because each element only
contains one type of atom, so all the
atoms in an element are identical.
● Have chemical properties, which are
characteristics or behaviours that may
be observed when the substance
undergoes a chemical change or
reaction.
What is a molecule?
●
●
●
Molecules form when two or more atoms
form chemical bonds with each other. It
doesn't matter if the atoms are the same
or are different from each other.
Molecules made up of two or more
elements are called compounds. Water,
calcium oxide, and glucose are molecules
that compound. All compounds are
molecules; not all molecules are
compounds.
Single atoms of elements are not
molecules. A single oxygen, O, is not a
molecule. When oxygen bonds to itself
(e.g., O2, O3) or to another element (e.g.,
carbon dioxide or CO2), molecules are
formed.
Molecules vs Compounds vs
Mixtures
Cognito
REACTIONS
Oxidation
Oxidation = gain of oxygen /
loss of electrons
Reduction
Reduction = loss of oxygen /
gain of electrons
Redox
Redox reaction & simultaneous
oxidation and reduction
INSIDE ATOMS
PROTON NUMBER AND MASS NUMBER
● Proton number = atomic
number it is represented by a Z
● Neutrons and protons have a
similar mass whereas
electrons possess very little
mass
● The total number of protons
and neutrons found in the
nucleus of an atom is called
the mass number (also called
nucleon number) and is
represented by A
IONS
● An ion is an electrically charged
particle.
● When an atom loses one or more
electrons, it is no longer electrically
neutral and becomes a positively
charged ion. This is called a cation.
● When an atom gains one or more
electrons, it becomes a negatively
charged ion. It is called an Anion
● The process of gaining or losing
electrons is known as ionisation.
ISOTOPES
●
●
●
Isotopes: different atoms of the same
element that have the same number
of protons but different numbers of
neutrons.
The isotopes of an element have the
same chemical properties because
they contain the same number of
outer shell electrons and therefore
have the same electronic
configuration.
Radioisotopes: certain isotopes such
as Carbon-14 and Tritium have a
nucleus so heavy that they are
radioactive in nature. Their nucleus is
unstable and breaks up
spontaneously.
RELATIVE ATOMIC MASS
Most elements exist naturally as a mixture of their isotopes. Using the data on the
abundance of these naturally occurring isotopes, we can calculate the relative atomic mass
of the element.
Isotopes and Relative Atomic
Mass
Cognito
Balancing Equations
Cognito
THANKS
Credits:
Cognito
Chem TB
Z notes
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